The present invention relates to a bearing apparatus, and more particularly to a bearing apparatus comprised of a split-type rolling bearing and a housing which supports the rolling bearing.
In an engine of such as an automobile or a marine vessel, a bearing for supporting a crankshaft which converts the reciprocating motion of a piston into rotational motion is disposed between adjacent counterweights or between a counterweight and a large end of a connecting rod, so that a split bearing which is circumferentially split in two halves is used.
Sliding bearings have generally been used as the aforementioned supporting bearings. However, since there has been an increasing demand for engines with less fuel consumption in recent years, the use of rolling bearings which are circumferentially split in place of the aforementioned sliding bearings has been proposed to reduce the rotational loss.
This split-type rolling bearing has, for example, a pair of split outer ring halves, a plurality of rollers disposed so as to be capable of rolling on the respective inner diameter surfaces of the both split outer ring halves, and a pair of split cage halves for retaining the respective rollers so as to dispose them at substantially equal intervals in the circumferential direction. Further, a crankshaft is fitted in the rolling bearing as an inner ring member, and the rolling bearing is incorporated in the large end of the connecting rod.
With such a rolling bearing, when it is incorporated into the large end of the connecting rod, there are cases where a radial offset (stepped portion) occurs at joint surfaces of the mutually opposing split outer ring halves. If the positional offset occurs at the split outer ring halves, there is a possibility that noise and vibration can be generated when the rollers roll over the vicinities of the joint surfaces of the outer ring where this positional offset occurred.
With rolling bearings, to allow the rolling elements to roll smoothly on the raceway surfaces, it is practiced to form an oil film on the raceway surfaces by supplying lubricating oil into the space where the rolling elements roll, to thereby alleviate the impact during the rolling of the rolling elements. FIG. 5 shows a related bearing apparatus which is provided with an oiling passage for such oil filling.
As shown in FIG. 5, this bearing apparatus has an engine crankshaft fixing portion 40 which is a housing. The crankshaft fixing portion 40 includes an upper block 41 having a semicircular recessed portion 41a as well as a lower block 42 having a semicircular recessed portion 42a and adapted to be integrally joined to the upper block 41. A supporting hole 43 for supporting a split-type rolling bearing 50 in close contact therewith is formed by the both semicircular recessed portions 41a and 42a. The upper block 41 and the lower block 42 are integrally fixed by fixing bolts 44.
An oiling passage 45 for supplying lubricating oil to the split-type rolling bearing 50 is formed in the upper block 41. This oiling passage 45 is formed in such a manner as to extend from diagonally above (diagonally above in FIG. 5) through the upper block 41 and to be open to the aforementioned supporting hole 43. Further, the split-type rolling bearing 50 is disposed in the supporting hole 43 in close contact therewith, and a crankshaft 46 is fitted in this split-type rolling bearing 50.
The split-type rolling bearing 50 has a pair of split outer ring halves 51a and 5b, a plurality of rollers 53 disposed so as to be capable of rolling on an outer ring raceway surface 52 formed on respective inner diameter surfaces of the split outer ring halves 51a and 51b, and a pair of split cage halves 54a and 54b for retaining the respective rollers 53 so as to dispose them at substantially equal intervals in the circumferential direction.
Further, an oil hole 55 is formed in one split outer ring half 51a, which is disposed on the upper side, in such a manner as to communicate with the aforementioned oiling passage 45 and to penetrate the split outer ring half 51a in the radial direction.
In addition, the circumferential both ends of both split outer ring halves 51a and 51b abut against each other, and these abutment surfaces constitute joint surfaces (i.e., mating plates) 57 and 58. Stepped portions such as the one described above can possibly occur at such joint surfaces 57 and 58.
As lubricating oil is supplied to the rollers 53 or the raceway surfaces through the oiling passage 45 such as the one shown in FIG. 5, an oil film is formed on the relevant raceway surfaces, and the impact during the rolling of the rollers 53 is alleviated by this oil film.
It is expected that the vibration and noise when the rollers 53 pass the stepped portions at the joint surfaces 57 and 58 are alleviated by sufficiently supplying lubricating oil. With the related bearing apparatus, however, the vibration and noise occurred due to the following reasons.
Namely, since the oil hole 55 is formed at a position opposing the oiling passage 45 formed in the upper block 41, the oil hole 55 is at a position distant from the joint surfaces 57 and 58, particularly the joint surface 58. This joint surface 58 is at a position distant from the oil hole 55 in an opposite direction to the rotating direction (see arrow Y in FIG. 5) of the crankshaft 46, i.e., at a position distant from the oil hole 55 by an angle of more than 180° in the rotating direction of the crankshaft 46.
For this reason, the lubricating oil which is supplied from the oil hole 55 cannot be sufficiently supplied to the outer ring raceway surface 52 in the vicinities of the mating plates 57 and 58, particularly the mating plates 58. As a result, an oil film with a thickness of such an extent as to make it possible to alleviate the impact of the rollers 53 rolling in the vicinities of these mating plates 58 is not formed on the outer ring raceway surface 52 in the vicinities of the mating plates 58.
In addition, in the split-type rolling bearing 50 shown in FIG. 5, its upper portion and lower portion constitute a loaded zone (side which is subjected to a load) of the bearing, and since the aforementioned oil hole 55 is provided in that loaded zone, the following problem is encountered.
Namely, the rollers 53 rolling in the loaded zone are subjected to a greater load than the rollers 53 rolling in a nonleaded zone, and if the oil hole 55 is formed in this loaded zone, a stress concentration occurs at the peripheral edge of the oil hole 55 when the rollers 53 pass the outer ring raceway surface 52 including the oil hole 55. As the stress is applied to the peripheral edge in a concentrated manner, there is a possibility of a decline in the service life of the bearing.